Multi-spectral, selectively reflective construct

ABSTRACT

A selectively reflective construct, and a method for making the construct, are described. In one embodiment reflectance, transmission and absorption properties may be controlled in multiple electromagnetic bands. A construct is described comprising a) a thermally transparent, visually opaque substrate comprising a polymeric material and a colorant, and b) a thermally reflective layer comprising a low emissivity component which is optionally transparent to radar signal.

CROSS REFERENCE TO RELATED CASES

This patent application is a divisional application of pendingapplication U.S. Ser. No. 12/391,595 filed Feb. 24, 2009; which claimsthe benefit of pending application U.S. Ser. No. 12/195,794, filed Aug.21, 2008; which further claims benefit of provisional application U.S.Ser. No. 60/986,741, filed Nov. 9, 2007.

FIELD OF THE INVENTION

This invention relates to a selectively reflective construct,controlling reflectance and transmission in the visible, nIR, SWIR,MWIR, LWIR, and radar bands of the EM spectrum.

BACKGROUND OF THE INVENTION

Camouflage materials used by hunters and by the military typicallyprovide camouflage properties in the visible portion of theelectromagnetic (EM) spectrum. Recent improvements to militarycamouflage have extended performance into the nIR portion and the shortwave infrared (SWIR). Due to the increased use of thermal imagingsensors operating in the mid wave infrared (MWIR) and long wave infrared(LWIR) EM bands, military users have sought enhanced protection in thesesensor bands.

Conventional means for achieving camouflage performance in the thermalbands often creates higher reflectance in the visible and nIR bands ofthe EM spectrum. Likewise, performance in the visible and nIR bandsoften increases detection in the thermal bands. Thus, an effectivemulti-spectral (visible, nIR, SWIR, MWIR, LWIR) solution has not beenavailable to control reflectance, transmission and absorption propertiesin a single construct throughout these distinct bands of the EMspectrum.

SUMMARY OF THE INVENTION

A construct is described wherein reflectance, transmission andabsorption properties may be controlled in multiple EM bands includingvisible, nIR, MWIR and LWIR. For the purposes of this invention, visibleis defined as 400-600 nm, nIR is defined to be 700-1000 nm, MWIR isdefined to be 3-5 μm, and LWIR is defined to be 9-12 μm. Methodsdescribed herein may also be suitable for forming constructs havingsuitable properties in the 8-14 μm wavelength range.

In one embodiment, a construct is described comprising a) a firstcomponent that is a thermally transparent, visually opaque substratecomprising a polymeric layer and colorant, and b) second component thatis a thermally reflective layer comprising a low emissivity componentadjacent a surface of the thermally transparent, visually opaquesubstrate. The construct has an average reflection of i) less than about70% in the wavelength range of 400-600 nm, ii) less than about 70% inthe wavelength range of 700-1000 nm, iii) greater than about 25% in thewavelength range of 3-5 μm, and iv) greater than about 25% in thewavelength range of 9-12 μm.

Constructs are described that are both thermally reflective and radarreflective. Other embodiments are described that are thermallyreflective and radar transparent. Some constructs transmit radar wavesthrough the construct thickness, while providing attenuation in multipleportions of the electromagnetic spectrum such as vis, nIR, SWIR, MWIRand/or LWIR. Some constructs can have 0% transmission at 1 to about 100GHz, while other constructs provide 100% transmission at 1 to about 100GHz. A construct will be considered radar transparent herein, if it iscapable of transmitting radar waves in a manner which provides anaverage radar transmission of greater than 90% throughout the frequencyrange of 1 to about 5 GHz. A construct may also be made having a radartransmission greater than 90% throughout the frequency range of 1 toabout 20 GHz, and/or also, a transmission of greater than 90% throughoutthe frequency range of 1 to about 100 GHZ.

In one embodiment a construct is provided that has an average reflectionof i) less than about 70% in the wavelength range of 400-600 nm, ii)less than about 70% in the wavelength range of 700-1000 nm, iii) greaterthan about 25% in the wavelength range of 3-5 μm, and iv) greater thanabout 25% in the wavelength range of 9-12 μm; and v) an average radartransmission greater than 90% throughout the frequency range of 1-5 GHz.A radar transparent construct may be provided in a location positionedbetween a radar sensor or detector and a radar camouflaged article.Alternatively, a radar camouflaging layer that absorbs, reflects orscatters radar signal may be used in combination with a radartransparent construct.

A method for multi-spectrally camouflaging a surface or object isdescribed which comprises the steps of a) providing a thermallytransparent, visually opaque substrate comprising a polymeric materialand a colorant; b) providing a thermally reflective layer comprising alow emissivity surface; c) disposing the low emissivity surface adjacentthe thermally transparent, visually opaque substrate to form amulti-spectral, selectively reflective construct; and d) positioning themulti-spectral, selectively reflective construct between a detectionmeans and an object being viewed.

BRIEF DESCRIPTIONS OF FIGURES

FIG. 1 is a cross-sectional view of a schematic of a selectivelyreflective construct

FIG. 2 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 3 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 4 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 5 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 6 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 7 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 8 is a cross-sectional view of a schematic of a selectivelyreflective construct.

FIG. 9 is a reflectance spectra of several examples of constructs from250 nm to 2,500 nm wavelengths.

FIG. 10 is a reflectance spectra of several example constructs from 3.0μm to 5.0 μm wavelengths.

FIG. 11 is a reflectance spectra of several example constructs from 8.0μm to 12.0 μm wavelengths.

FIG. 12 is a cross-sectional view of a schematic of a selectivelyreflective construct further comprising a radar camouflaging layer.

DETAILED DESCRIPTION OF THE INVENTION

Multi-spectral, selectively reflective constructs are described withreference to FIGS. 1-8. For the purposes of this invention, visible isdefined as 400 nm-600 nm, nIR is defined to be 700 nm-1000 nm, MWIR isdefined to be 3 μm-5 μm, and LWIR is defined to be 9 μm-12 μm. MWIR andLWIR spectral response represents the thermal region.

As exemplified by the cross-sectional view of the schematic constructillustrated in FIG. 1, in one embodiment a construct (10) comprises afirst component comprising a thermally transparent, visually opaquesubstrate (1) having a first surface (12) and a second surface (13); anda second component comprising a thermally reflective layer (30). Thethermally reflective layer (30) comprises a low emissivity component,and is adjacent the second surface (13) of the thermally transparent,visually opaque substrate (1). The multi-spectral, selectivelyreflective construct has an average reflection of: i) less than about70% in the wavelength range of 400 nm to 600 nm; ii) less than about 70%in the wavelength range of 700 nm to 1000 nm; iii) greater than about25% in the wavelength range of 3 μm to 5 μm; and iv) greater than about25% in the wavelength range of 9 to 12 μm.

In a further embodiment, a multi-spectral, selectively reflectiveconstruct is made having an average reflection of: i) less than about50% in the wavelength range of 400 nm to 600 nm; ii) less than about 70%in the wavelength range of 700 nm to 1000 nm; iii) greater than about25% in the wavelength range of 3 μm to 5 μm; and iv) greater than about25% in the wavelength range of 9 μm to 12 μm. Another construct may beprepared having an average reflection of: i) less than about 70% in thewavelength range of 400 nm to 600 nm; ii) less than about 50% in thewavelength range of 700 nm to 1000 nm; iii) greater than about 25% inthe wavelength range of 3 μm to 5 μm; and iv) greater than about 25% inthe wavelength range of 9 μm to 12 μm. Further embodiment may beprepared wherein the multi-spectral, selectively reflective constructhas an average reflection of: i) less than about 70% in the wavelengthrange of 400 nm to 600 nm; ii) less than about 70% in the wavelengthrange of 700 nm to 1000 nm; iii) greater than about 25% in thewavelength range of 3 μm to 5 μm; and iv) greater than about 35% in thewavelength range of 9 μm to 12 μm.

Further with regard to FIG. 1, the construct (10) comprises a firstcomponent that is a thermally transparent, visually opaque substrate (1)that is optically colored. The thermally transparent, visually opaquesubstrate (1) is comprised of a polymeric material (2) and a colorant(60). To form a thermally transparent substrate, the polymeric material(2) is comprised of a polymer having high transmission in the 3 μm-5 μmand 9 μm-12 μm bandwidths. The thermally transparent, visually opaquesubstrate (1) will be considered thermally transparent if it has aaverage transmission greater than about 30% at 3 μm to 5 μm (MWIR) and 9μm to 12 μm (LWIR). In some embodiments, constructs are formed having athermally transparent, visually opaque substrate having an averagetransmission of greater than or equal to about 40%, 50%, 60% or 70% inthe wavelength range of 3 to 5 μm and/or an average transmission ofgreater than or equal to about 40%, 50%, 60% or 70% in the wavelengthrange of 9 μm to 12 μm.

The polymeric material (2) of the thermally transparent, visually opaquesubstrate (1) may include polytetrafluoroethylene (PTFE), microporousexpanded PTFE (ePTFE), fluorinated ethylene propylene (FEP),perfluoroalkoxy copolymer resin (PFA), and polyolefins, includingpolypropylene and polyethylene. The polymeric material may be porous ormicroporous, or monolithic. The term microporous, as used herein, candescribe the structure of microporous polymer layers having a node andfibril microstructure similar microporous polymeric materials describedin and formed by the methods described in U.S. Pat. No. 3,953,566, thedescription and methods of which are hereby incorporated by reference.Other suitable microporous polymeric layers may a microstructure similarto that depicted in U.S. Pat. Nos. 4,539,256; 4,726,989; or 4,863,792,which are also incorporated by reference. A microporous structure of apolymer introduces many polymer/air interfaces (e.g. pores) that reducethe optical transparency of the polymer in the visible wavelengthregion. This can increase the whiteness of an otherwise clear ortranslucent polymer layer.

The polymeric materials may be a continuous or discontinuous polymericfilm. The polymeric material comprises a polymeric layer which maycomprise polymeric films or fibers. Material thickness, index ofrefraction, and porosity of the polymeric material (2) may be selectedto achieve desired levels of visual opacity and thermal transparency.Polymeric layers having thickness of greater than 5 microns (μm) may besuitable for certain applications. In other embodiments, polymericlayers greater than about 20 μm, greater than about 40 μm, or greaterthan about 100 μm may be suitable.

The first component comprising the thermally transparent, visuallyopaque substrate will be considered visually opaque when the opticaldensity is greater than about 0.30 between 475 nm and 675 nm, whenmeasured according to the method described herein. In other embodimentsconstructs may have thermally transparent, visually opaque substrateshaving optical densities greater than about 0.70, greater than about0.75, or greater than about 1.0, between 475 nm and 675 nm. Embodimentswherein the thermally transparent, visually opaque substrate has opticaldensity greater than about 1.5, greater than about 2, or greater thanabout 3, between 475 nm and 675 nm, may also be considered useful.Specific optical densities, thermal and nIR properties may be achievedby the combination of polymeric material (2) and colorant (60).

Microporous polymeric films may be particularly suitable where theporosity of the film is selected to contribute to the desired level ofvisual opacity. In one embodiment exemplified by FIG. 6, a firstcomponent is a thermally transparent, visually opaque substrate (1)comprising a microporous polymeric material (2). Microporous polymericfilms having a thickness ranging from about 5 μm-300 μm may be suitablefor certain constructs used herein. For example, a construct maycomprise a thermally transparent, visually opaque substrate thatcomprises a microporous polytetrafluoroethylene (ePTFE) film having athickness less than about 50 microns and having an optical densitygreater than about 0.50. In one particular embodiment, a thermallytransparent, visually opaque substrate comprises a microporouspolytetrafluoroethylene (ePTFE) film approximately 35 microns thick withan optical density of 0.77. Alternately, a construct may comprise athermally transparent, visually opaque substrate comprising amicroporous ePTFE film having a thickness less than about 120 micronswith an optical density greater than about 0.90. In a particularembodiment, a thermally transparent, visually opaque substrate comprisesa microporous ePTFE film that is approximately 110 microns thick with anoptical density of about 1.1.

Colorant may be used to affect the visible, nIR, and SWIR spectralresponse. The colorant (60) may be comprised of one or more additivesthat absorb, refract, and/or reflect light. The colorant (60) may bedisposed on either the first surface (12) or second surface (13) of thepolymeric material (2), within the polymeric material, or disposed onboth the first and second surfaces and within the polymeric material.The colorant may comprise one or more dyes including, but not limited toacid dyes, disperse dyes, mordant dyes, and solvent dyes. The colorantmay comprise one or more pigments including, but not limited to carbonpigments, cadmium pigments, iron oxide pigments, zinc pigments, arsenicpigments, and organic pigments. The colorant may be applied as an ink,toner, or other appropriate print media to deliver the dye or pigmentonto or into the polymeric substrate. Ink suitable for use in thepresent invention may be solid, aqueous, or solvent based.

The colorant (60) may comprise a single colorant or the colorant may becomprised of one or more colorants (60, 61, 62, and 63), for example, asa blend of more than one colorant. In a further embodiment, the firstcomponent comprising the thermally transparent, visually opaquesubstrate (1) may comprise multiple colorants (61, 62, 63) and themultiple colorants may be applied in discrete patterns as depicted inFIG. 3, or a pattern such as a camouflage pattern. Where disposed on asurface of the first component, such as the first surface (12) of thepolymeric material (2) as depicted in FIG. 4, the multiple colorants(61, 62, 63) may be bonded to the polymeric material, for example, bythe selection of dyes with the appropriate bond sites, or by use ofbinders which affix the colorant to the polymeric material. As usedherein, the first surface (12) of the polymeric material (2) refers tothe surface oriented outwardly, away from a wearer or object to beshielded from detection, or the surface of the polymeric material facingin the direction of an EM sensor or detector. As depicted in FIG. 6, thecolorant (60) may be imbibed into the polymeric material (2), and maycoat the pore walls of a porous polymeric material. Alternately,colorant (60) may be added as a filler to the polymeric material (2).

To obtain the desired visual opacity of the first component comprisingthe thermally transparent, visually opaque substrate (1), properties ofthe polymeric material (2), such as material thickness, index ofrefraction, and porosity, are balanced. In certain embodiments wherethinner materials are preferred, for example for added flexibility,thinner materials may be too visually transparent to achieve the desiredproperties of the final construct. Therefore, in some embodiments visualopacity may be increased by increasing porosity. Visual opacity within adesired range may also be achieved by the selection and concentration ofcolorant (60) in combination with the selection of the polymericmaterial (2). For example, where a polymeric material is selected havingan optical density less than about 0.30, a colorant may be added toincrease the optical density, so that the thermally transparent,visually opaque substrate comprising the polymeric material and coloranthas an optical density greater than about 0.30. Both colorant type andconcentration may be selected to achieve the desired visual opacity ofthe first component comprising the thermally transparent, visuallyopaque substrate (1). In one embodiment a first component comprises amicroporous polytetrafluoroethylene (ePTFE) layer approximately 35microns thick with an optical density of 0.77. In another embodiment afirst component comprises a microporous ePTFE layer approximately 110microns thick with an optical density of about 1.1.

In one embodiment, a construct which comprises a first component that isa thermally transparent, visually opaque substrate comprising amicroporous ePTFE layer approximately 35 microns thick and a carboncolorant, has an optical density greater than 1.5. In anotherembodiment, a construct is formed wherein the thermally transparent,visually opaque substrate comprises a microporous ePTFE and colorant,having an optical density greater than 4.0; in an alternate embodimentcomprising a similar colorant, a thermally transparent, visually opaquesubstrate comprising a visually transparent monolithic polyethylenepolymeric layer has an optical density of greater than 1.0.

In addition to providing performance in the visible region of the EMspectrum, constructs may be formed having specific levels of reflectionand absorption in the near-infrared (nIR) region of the EM spectrum.Preferred constructs have a reflectance of less than 70% in thewavelength range of 700 μm-1000 μm. A thermally transparent, visuallyopaque substrate comprising a polymeric material may be formed having adesired level of nIR reflection. To achieve a desired level of nIRreflection in the final construct, the level of nIR reflection of thefirst component may be adjusted to account for effects that result fromthe addition of the other layers of the construct.

In some embodiments, the colorant (60) is selected to achieve aparticular nIR reflectance in addition to the desired visiblereflectance of the selectively reflective construct (10). For example,reflecting and absorbing additives may be selected as a colorant andapplied to the polymeric material (2) of the first component in a mannerto achieve a desired level of both the color (visible) and nIRreflectance. In one embodiment, a first component comprising amicroporous material, such as ePTFE, may be formed comprising nIRadditives, such as carbon. The polymeric material used to form themicroporous material may comprise one or more nIR additives, and canthen be formed into a thermally transparent microporous film having adesired level of nIR reflection. nIR additives (90, 91, 92, 93) such asbut not limited to carbon, metal, and TiO₂ can be added to the thermallytransparent, visually opaque first substrate (1) to achieve specificnIR, SWIR, MWIR, or LWIR reflectance properties as illustrated in FIGS.2 and 4.

Specific reflectance properties of the construct in the short waveinfrared (SWIR) can also be obtained through the use of infrared (IR)additives, adjusting the pore size of the polymeric material, and/oradjusting the thickness of the polymeric material. Suitable performancefor constructs has less than 70% reflectance in the SWIR (900 nm to 2500nm).

Measurements of average thermal emissivity over broad spectral bandssuch as 3 μm-30 μm, are suitable for characterization of the thermallyreflective layer. However, broad band measurements do not adequatelycharacterize the specific performance of a construct in use. Constructsdescribed herein are designed to provide specific spectral performancein narrower regions of interest, such as performance averaged over thewavelength range of 3 μm-5 μm (MWIR) or averaged over the wavelengthrange of 9 μm-12 μm average (LWIR). In some embodiments, specificspectral performance can be tailored to particular reflectances atspecific wavelengths of interest within these ranges. Reflectance ortransmission within the narrower ranges of 3 μm-5 μm and/or 9 μm-12 μmis considered thermal performance.

In one embodiment a multi-spectral, selectively reflective construct isprovided having a thermal performance of an average reflectance ofgreater than or equal to about 25%, in the wavelength range of 3 μm to 5μm, and/or an average reflectance of greater than or equal to about 25%reflectance in the 9 μm to 12 μm. In other embodiments, constructs areformed having an average reflectance of greater than or equal to about30%, 40%, 50%, or 60% in the wavelength range of 3 μm to 5 μm, and/or anaverage reflectance of greater than or equal to about 30%, 40%, 50%, or60% in the wavelength range of 9 μm to 12 μm. In certain embodiments,multispectral, selectively reflective constructs have a reflectancegreater than 30% and less than 98%, less than 90%, or less than 80% inthe wavelength ranges of 3 μm to 5 μm and/or 9 μm to 12 μm, whenmeasured according to the test methods described herein.

Further with regard to FIG. 1, the multi-spectral, selectivelyreflective construct (10) comprises a second component comprisingthermally reflective layer (30) comprising a low emissivity component(35) which imparts a high reflectance to the construct in the wavelengthranges of 3 μm to 5 μm and 9 μm to 12 μm. The thermally reflective layerhas an emissivity of less than about 0.75, less than about 0.6, lessthan about 0.5, less than about 0.4, less than about 0.3, or less thanabout 0.2, when tested according to the Emissivity Measurement testmethod described herein. The low emissivity component (35) may be acoating or substrate with emissivity of less than about 0.75. Lowemissivity components comprise metals including, but not limited to Ag,Cu, Au, Ni, Sn, Al, and Cr. Additionally, low emissivity components maycomprise non-metal materials having an emissivity of less than about0.75, less than about 0.6, less than about 0.5, less than about 0.4,less than about 0.3, or less than about 0.2, when tested according tothe Emissivity Measurement test method described herein. Non-metalmaterials which may be suitable for use in the low emissivity componentinclude indium-tin oxide, carbon nanotubes, polypyrol, polyacetylene,polythiophene, polyfluorene, and polyaniline. The thickness of thethermally reflective layer (30) may be selected to achieve certainproperties. In one embodiment, where a flexible multi-spectral,selectively reflective construct is desired, the thickness of thethermally reflective layer (30) comprising a low emissivity componentmay be minimized, and a thermally reflective layer having a thickness ofless than about 0.002 inch may be selected.

In one embodiment, the thermally reflective layer (30) may be comprisedof a low emissivity component applied to the second surface (13) of thethermally transparent, visually opaque substrate (1) by metal vapordeposition or by a spray coating containing metal particles, such as ametallic spray paint. In a further embodiment, the thermally reflectivelayer (30) may be formed by bonding a low emissivity component (35) tothe second surface (13) of the thermally transparent, visually opaquesubstrate (1), with an intervening layer (4), such as an adhesive orspacer material, as exemplified in FIG. 1. The thermally reflectivelayer (30) may comprise a low emissivity component, for example, in theform of a transfer foil.

In an alternate embodiment, such as exemplified in FIGS. 6 and 7, athermally reflective layer (30) may comprise a low emissivity component(35) such as metal containing film, or a metal spray painted film whichmay be disposed behind or adhered to the second surface (13) of thethermally transparent, visually opaque substrate (1). The metallizationof a suitable film can be accomplished by electroless platingtechniques, by vapor deposition, or by the reduction of metal salts inor on the surface of a film.

Alternatively, metal-containing films suitable for this invention can beformed by metal-filled polymer extrusion, metal surface impregnation, orthe lamination or encapsulation of metal films or particles. Forexample, as exemplified in FIG. 8, a construct (10) may comprise a firstcomponent (80) comprising a first substrate (81) that is the thermallytransparent, visually opaque substrate, and a second component (70)comprising a second substrate (71). The second component (70) comprisinga thermally reflective layer comprises a substrate (71), for example, afilm such as expanded PTFE that has been metallized with a lowemissivity component (35) and is adhered by an intervening layer (4) tothe second surface (13) of the thermally transparent, visually opaquefirst substrate (81). In another embodiment, the second component (70)may comprise a metallized textile disposed adjacent the second surface(13) of the thermally transparent, visually opaque first substrate (81),and optionally attached to the first substrate (81).

In one embodiment, where the thermally reflective layer (30) is formedby affixing a low emissivity component to the second surface (13) of thethermally transparent, visually opaque substrate (1), an interveninglayer (4) that is either continuous or discontinuous may be used. Amulti-spectral, selectively reflective construct comprising a continuousthermally transparent intervening layer (4), such as an adhesive orspacer material, is exemplified in FIG. 1. Alternately, a discontinuousintervening layer (4) having sufficient thermal transparency to achievethe desired thermal properties of the multi-spectral, selectivelyreflective construct may be used. Multi-spectral, selectively reflectiveconstructs having a discontinuous intervening layer (4), for example,are exemplified in FIGS. 2, 4, 5, 7, and 8.

In another embodiment, a multi-spectral, selectively reflectiveconstruct is provided wherein a second component comprising thethermally reflective layer (30) comprising a low emissivity component ispositioned adjacent the second surface of the first component comprisingthe thermally transparent visually opaque substrate (1) with little orno attachment to the thermally transparent, visually opaque substrate.In one embodiment, a construct may be formed similar to the constructillustrated in FIG. 1, with no intervening layer (4). Adjacent, as usedin the context of the present invention, means either (a) locatedimmediately next to with no intervening layers, (b) adhered directly to,(c) adhered to with intervening layers, or (d) located on a particularside but separated from the other layer by intervening layers of anothermaterial. Provided the desired multi-spectral performance of the presentinvention is achieved, an embodiment can be made having one or moreintervening layers of sufficiently thermally transparent materiallocated between the second surface (13) of the thermally transparent,visually opaque substrate (1) and the thermally reflective layer (30).These layers can be either adhered to each other or not adhered to eachother, or any combination thereof.

The thermally reflective layer may comprise a low emissivity componenthaving a single emissivity over the entire surface of the thermallyreflective layer (30), or alternately, a range of emissivities may beprovided. In one embodiment, as exemplified in FIG. 7, the thermallyreflective layer (30) may comprise multiple discrete low emissivitycomponents (31, 32, 33) adjacent the second surface (13) of thethermally transparent, visually opaque substrate (1). In one embodimentthe thermally reflective layer (30) may comprise a single continuouslayer of a low emissivity component, or in an alternate embodiment, thethermally reflective layer (30) may comprise a discontinuous pattern oflow emissivity components.

In some embodiments, the multi-spectral, selectively reflectiveconstruct (10) is thermally reflective and radar reflective. In otherembodiments, the multi-spectral, selectively reflective construct (10)may be constructed to be thermally reflective while also beingtransparent to radar signal. Constructs may also be formed which arecapable of transmitting radar waves, while providing attenuation inmultiple portions of the electromagnetic spectrum such as vis, nIR,SWIR, MWIR and/or LWIR Some constructs can have 0% transmission at 1 toabout 100 GHz, while other constructs provide 100% transmission at 1 toabout 100 GHz.

A construct will be considered radar transparent, herein, if it iscapable of transmitting radar waves and where the average of thetransmission data collected in the range of 1 GHz to about 5 GHz isgreater than about 90%, when tested according to the method providedherein. In other embodiments, a multi-spectral, selectively reflectiveconstruct (10) may be formed having an average radar transmission ofgreater than 90% the range from 1 to about 20 GHz, when tested accordingto the method provided herein, and/or an average transmission greaterthan 90% the range from about 1 to about 100 GHz. Constructs may also beformed having an average transmission greater than 95%, or greater than98%, or greater than 99%, in the ranges from 1 GHz to about 5 GHz, or 1GHz to about 20 GHz, when tested according to the methods providedherein.

Advantageously, in certain embodiments, constructs (10) are providedwhich are thermally protective, having an average reflection of greaterthan 25% in the wavelength ranges of 3 um-5 um, 9 um-12 um, or both MWIRand LWIR wavelength ranges, while also having a radar transmissiongreater than 90%, or greater than 95%, or greater than 98% or greaterthan 99%, throughout the frequency ranges of 1-5 GHz, 1-20 GHz, or bothranges, when tested according to the methods provided herein for thermalreflection and radar transparency.

One radar transparent, multi-spectral selectively reflective constructsuitable for use in providing detection protection comprises a firstsubstrate comprising a microporous polymeric substrate having a coloranton at least a first surface and a second surface that is opposite thefirst surface. A second substrate is provided that comprises ametallized film or transferred metallized film, wherein the firstsubstrate and the second substrate are arranged so that the metal of themetallized film is oriented toward a second surface of the firstsubstrate. In one embodiment, the second substrate is a metallizedmicroporous polymeric substrate. The metal of the metallized film maycomprise, for example, at least one of, but not limited to, aluminum(Al), copper (Cu), gold (Au), silver (Ag), nickel (Ni), tin (Sn), zinc(Zn), lead (Pb), and chromium (Cr), and alloys thereof. Where radartransparency is desired, it may be desirable for the metal layerdeposited on a polymeric substrate to have a thickness of less than 1μm, less than 500 nm, less than 400 nm, or less than 200 nm, when testedaccording to the method provided herein for determining metal thickness.The first and second substrates may be affixed, such as by sewing,lamination, or otherwise adhering the two substrates together. Theconstruct may further be laminated to a textile backer layer.

One embodiment described herein comprises construct comprising a frontsurface and a back surface, a first substrate and a second substrate,where both substrates comprise microporous expandedpolytetrafluoroethylene (ePTFE). In one embodiment, the first substratecomprises a thermally transparent visually opaque layer that has a firstsurface that is comprised of microporous ePTFE comprising a colorant andcorresponds to the front surface of the construct, and a second surface.The second substrate comprises a metallized ePTFE, wherein the metal maycomprise, for example, vapor deposited metal in one embodiment, or metaldeposited by spray in another embodiment. The first and secondsubstrates are arranged so that the metallized surface of the secondePTFE layer is adjacent the second surface of the first substrate.

Advantageously, constructs can be formed that are oleophobic, having anoil rating greater than 1, or greater than 2, or greater than 3, orgreater than 4, or greater than 5, or greater than 6.

Importantly, constructs of the present invention can be formed that arelightweight, weighing less than 200 grams per square meter (gsm). Somepreferred multi-spectral, selectively reflective constructs of thepresent invention may weigh less than 150 gsm, preferably less than 100gsm, and more preferably less than 50 gsm. In some instances wheregreater durability is desired, a heavier weight backer is used whichwill increase the total construct weight. For example, in oneembodiment, a 250 gsm backer textile applied to a construct provides atotal construct weight that may be between about 270 gsm and 450 gsm.

Protective coverings can be made from a radar transparent,multi-spectral, selectively reflective construct (10) for coveringarticles such as, for example, equipment, shelters such as tents, andvehicles that are already provided with radar camouflage. The protectivecovers can add visible, nIR, MWIR and/or LWIR signature protection to anarticle, while advantageously maintaining the radar signature reductioncapabilities of these articles due to the radar transparency of thecover.

In a further embodiment, a multi-spectral selectively reflectiveconstruct (10) that is radar transparent may comprise at least oneadditional layer (40) that is radar camouflaging as exemplified by thecross-sectional illustration of FIG. 12. By radar camouflaging, it ismeant that the at least one additional layer absorbs, reflects and/orscatters radar signal within the frequency range of about 1-5 GHz, about1-20 GHz, or about 1-100 GHz. The radar camouflaging layer may providecomplete absorption, reflection or scattering of the radar signal; orthe radar camouflaging layer may provide selective or patternedabsorption, reflection or scattering of the radar signal. The radarcamouflaging layer (40) may optionally be affixed to the multi-spectralselectively reflective construct (10) to the thermally reflective layer(30) by an attachment means (41). Attachment means may be by laminationtechniques, adhesive, sewing, and the like. Alternatively, the radarcamouflaging layer (40) may be a separate layer, separated from amulti-spectral, selectively reflective construct by air or other radartransparent layers. A variety of radar camouflaging layers may besuitable to provide protection depending upon the desired level of radarprotection. Materials which may be suitable include but are not limitedto carbon and/or metal powders that are incorporated, for example, as acoating on a substrate, fibers, foams, and/or polymeric composites.Examples may be found in U.S. Pat. Nos. 5,922,986; 5,312,678; 6,224,982;and 5,185,381.

For applications where properties are desired, such as liquidproofness,flame retardancy, or chemical and biological agent protection, themulti-spectral, selectively reflective construct may comprise one ormore substrate backers (5) adjacent the side of the thermally reflectivelayer (30) that is the side opposite the first substrate (1). Asexemplified in FIG. 5, a porous substrate backer (5) may optionally beprovided to one side of the thermally reflectively layer (30) of themulti-spectral, selectively reflective construct. This embodimentfurther enhances the utility of the present invention by providingenhanced properties to the construct independent of the visual, nIR andthermal reflection properties. As illustrated in FIG. 5, a textile layermay serve as a porous substrate backer (5), which may be attached byattachments (8), such as by adhesive bonds to the of the thermallyreflective layer, for example, to improve abrasion resistance or tearstrength. Textiles are particularly suitable for use as a poroussubstrate backer (5) and may be tailored to provide improved durability,structural or dimensional stability, flame retardancy, insulation, andthe like, to the multi-spectral, selectively reflective construct whilemaintaining comfort and aesthetics. Suitable textiles for such purposesinclude, but are not limited to, wovens, knits, and non-wovens. Inanother embodiment of the present invention, the porous substrate backer(5) may comprise a porous or microporous film such as expanded PTFE.Porous or microporous films can provide protection to the low emissivitylayer while maintaining breathability.

The construct breathability as measured by MVTR test method describedherein is desirably greater than 1,000 (g/m²/day). Breathability ofgreater than 2,000 (g/m²/day), greater than 4,000 (g/m²/day), greaterthan 6,000 (g/m²/day), greater than 8,000 (g/m²/day), and even greaterthan 10,000 (g/m²/day) can be achieved for constructs described herein.

The multi-spectral, selectively reflective construct (10) once assembledmay be used in a wide variety of applications including but not limitedto garments, coverings, shelters, hides, and netting. Articlescomprising these constructs may be made using a single ply of themulti-spectral, selectively reflective construct or with a plurality ofplies to provide the appropriate depth of view and reflectancecharacteristics. For example, in one embodiment of a garmentapplication, in which the wearer of a garment is to be concealed, it maybe advantageous to provide multiple layers of narrowly cutmulti-spectral, selectively reflective construct material (i.e. 1″×4″strips) on another layer of the selectively reflective construct whichforms the body of the garment. This provides for greater visualdisruption of the wearer's silhouette while providing enhanced thermalreflective performance.

Articles comprising the multi-spectral selectively reflective constructsare formed having a front surface and a back surface wherein the frontsurface is oriented towards the potential source of detection. The backsurface, which is opposite the front surface, is generally orientedtowards the object or body to be shielded from detection. The constructcomprises a first component that is the thermally transparent, visuallyopaque substrate, and a second component that is the thermallyreflective layer wherein the thermally transparent, visually opaquesubstrate is positioned between the source of detection and thethermally reflective layer. The thermally reflective layer is positionedbetween the thermally transparent, visually opaque layer and the objector body to be shielded from detection. Therefore, where the articlecomprises, for example, a tent, a garment, a shelter, or protectivecovering, the first component of the construct corresponds to, or isproximate, the outer surface of the article, and the second component ofthe construct corresponds to, or is proximate, the inner surface of thearticle and therefore, proximate the object or body to be shielded fromdetection.

The thermal performance properties of articles comprising themulti-spectral, selectively reflective constructs described herein maybe further enhanced by selectively applying insulating materials orinsulating composites between the wearer/equipment being protected fromthermal detection, and the multi-spectral, selectively reflectiveconstruct layer. For example, in one embodiment a garment is formedcomprising the multi-spectral selectively reflective composite thatfurther comprises an insulating material provided, for example, to areasof the garment corresponding to the shoulder area, to minimize hot spotson the garment, and reduce thermal signature. Where the need exists toreduce thermal signature over long periods of time (e.g., in excess of a24 hour period), high performing insulation materials, such as thosetaught in commonly owned U.S. Pat. No. 7,118,801, may be preferred.These insulation materials may also be suitable to mask hot portions ofthe equipment (such as the engine compartment) and may be used incombination with a cover made from the multi-spectral, selectivelyreflective construct material described herein which will further maskthermal signature and provide visual and nIR image suppression.

In alternate embodiments, the multi-spectral, selectively reflectiveconstruct of the present invention may have a thickness less than about20 mm, and preferably less than about 10 mm, and more preferably lessthan about 7 mm, and even more preferably less than about 5 mm. Wherethinner constructs are desired, a multi-spectral, selectively reflectiveconstruct may have a thickness less than about 3 mm, or even less than 1mm.

In alternate embodiments, the multi-spectral, selectively reflectiveconstruct of the present invention may have a weight less than about 20oz/yd², and preferably less than about 15 oz/yd², and more preferablyless than about 10 oz/yd², and even more preferably less than about 7oz/yd².

In alternate embodiments, the multi-spectral, selectively reflectiveconstruct of the present invention may have a hand less than about 3,000gm, and preferably less than about 2,000 gm, and more preferably lessthan about 1,000 gm, and even more preferably less than about 500 gm.Some multi-spectral, selectively reflective constructs of the presentinvention may have a hand less than about 300 gm, preferably less than150 gm, and more preferably less than 100 gm.

Test Methods

Liquidproof Test

Liquidproof testing was conducted as follows. Material constructionswere tested for liquidproofness by using a modified Suter test apparatuswith water serving as a representative test liquid. Water is forcedagainst a sample area of about 4¼-inch diameter sealed by two rubbergaskets in a clamped arrangement. For samples incorporating one or moretextile layers, a textile layer is oriented opposite the face againstwhich water is forced. When a non-textile sample (i.e., film notlaminated to a textile layer) is Suter tested, a scrim is placed on theupper face of the sample (i.e., face opposite the face against whichwater is forced) to prevent abnormal stretching of the sample whensubjected to water pressure. The sample is open to atmosphericconditions and is visible to the testing operator. The water pressure onthe sample is increased to about 1 psi by a pump connected to a waterreservoir, as indicated by an appropriate gauge and regulated by anin-line valve. The test sample is at an angle, and the water isrecirculated to assure water contact and not air against the sample'slower surface. The upper face of the sample is visually observed for aperiod of 3 minutes for the appearance of any water which would beforced through the sample. Liquid water seen on the surface isinterpreted as a leak. If no liquid water is visible on the samplesurface within 3 minutes the sample is considered as having passed theLiquidproof test (Suter test). A sample passing this test is defined as“liquidproof” as used herein.

Hand Test

Hand was tested on test samples using a Thwing-Albert Handle-O-Meter(model #211-5 from Thwing Albert Instrument Company, Philadelphia, Pa.).A set, beam load was used to force test specimens through a ¼ inch slot.A load of 1000 grams was used when testing laminate samples. Theinstrument measures the resistance force which is related to the bendingstiffness of the sample and displays the peak resistance digitally. Inorder to adequately quantify the directionality and the asymmetry of thesamples, different samples are cut for bending against the X-directionand Y-direction, respectively. Four inch squares are cut from thematerial to be tested.

In a typical test, an X-direction sample is placed on the equipment suchthat the X-direction runs perpendicular to the slot. With the sampleconstruct face up, the test is initiated, causing the beam to lower andthe sample to be forced through the slot on the test table. A peakresistance number is displayed and recorded as “sample construct faceup”. The same sample is subsequently turned over and rotated 180 degreesto bend a different site. In this new configuration, again the test isinitiated causing the sample to be forced through the slot. The secondresistance number is recorded as “sample construct face down”. Theprocedure is repeated for a Y-direction sample (in which the Y-directionis oriented perpendicular to the slot), generating two more numbers:“sample construct face up” and “sample construct face down”.

The resultant four numbers (X-direction and Y-direction, sampleconstruct face up and sample construct face down) are added to provide atotal hand number in grams (gm) which characterizes the stiffness of thesample (taking into account asymmetry and directionality). At least twosuch total hand numbers were generated and averaged to arrive at thereported hand number.

Moisture Vapor Transmission Rate (MVTR)

A description of the test employed to measure moisture vaportransmission rate (MVTR) is given below. The procedure has been found tobe suitable for testing films, coatings, and coated products.

In the procedure, approximately 70 ml of a saturated salt solutionconsisting of 35 parts by weight of potassium acetate and 15 parts byweight of distilled water was placed into a 133 ml polypropylene cup,having an inside diameter of 6.5 cm at its mouth. An expandedpolytetrafluoroethylene (PTFE) membrane having a minimum MVTR ofapproximately 85,000 g/m²/24 hrs. as tested by the method described inU.S. Pat. No. 4,862,730 (to Crosby), was heat sealed to the lip of thecup to create a taut, leakproof, microporous barrier containing thesolution.

A similar expanded PTFE membrane was mounted to the surface of a waterbath. The water bath assembly was controlled at 23° C. plus 0.2° C.,utilizing a temperature controlled room and a water circulating bath.

The sample to be tested was allowed to condition at a temperature of 23°C. and a relative humidity of 50% prior to performing the testprocedure. Samples were placed so the first substrate was oriented awayfrom the waterbath, and the opposing surface was in contact with theexpanded polytetrafluoroethylene membrane mounted to the surface of thewater bath and allowed to equilibrate for at least 15 minutes prior tothe introduction of the cup assembly. The cup assembly was weighed tothe nearest 1/1000 g and was placed in an inverted manner onto thecenter of the test sample.

Water transport was provided by the driving force between the water inthe water bath and the saturated salt solution providing water flux bydiffusion in that direction. The sample was tested for 15 minutes andthe cup assembly was then removed, weighed again within 1/1000 g.

The MVTR of the sample was calculated from the weight gain of the cupassembly and was expressed in grams of water per square meter of samplesurface area per 24 hours.

Reflectance Test Method for Visible and Near Infrared Spectra

The spectral near normal-hemispherical reflectance of the samples (forexample, the colored side of the first substrate of a construct) in thevisible and near infrared (nIR) spectral range was measured usingUV/VIS/nIR spectrophotometer (Perkin-Elmer Lambda 950) fitted with a 150mm diameter, integrating sphere coated with Spectralon® (Labsphere DRA2500) that collects both specular and diffuse radiation. The reflectancemeasurements are made with double beam mode of operation and Spectralon®materials were used as references from 250 nm to 2500 nm at 20 nmintervals.

The samples were measured as a single layer with a backer. The backersused were dull black coated polymer sheets. Measurements were taken on aminimum of three different areas and the data of the measured areas wasaveraged. In this work, all the measurements were performed for nearnormal incidence, i.e. the sample was viewed at an angle no greater than10 degrees from the normal, with the specular component included. ThePhotometric accuracy of the spectrophotometer was calibrated to within 1percent and wavelength accuracy within 2 nm with a standard aperturesize used in the measurement device. To compensate for the signal lossdue to the backer material, the sample reflectance was calculatedaccording to ASTM:E903-96 standard test method for Reflectance ofmaterials using integrating sphere.

The results from the spectrophotometer measurement in the visible andnear infrared ranges are reported in Table 1 in terms of averagehemispherical reflectance for a particular wavelength range. of all datapoints collected.

Test method for Hemispherical Reflectance and Transmittance Over theThermal Infrared Spectral Range

Spectral near normal-hemispherical transmittance and reflectance in thethermal infrared spectrum is of great importance for the design andevaluation of this invention. The measured hemispherical reflectance andtransmittance spectra can be used to compute directional emissivity viaKirchhoff's law (ε=1−R−T; for opaque substrates, ε=1−R [where ε isemittance, R is reflectance, & T is transmittance).

To measure the direction-hemispherical transmittance and reflection, thesamples were viewed at an angle no greater than 10 degrees from thenormal, with the specular component included. Measurements were made ofthe spectral hemispherical transmittance and reflectance of the samplesover the range 600 cm⁻¹ to 5000 cm⁻¹, with a spectral resolution of 8cm⁻¹. The optical radiation source and wavenumber selectivity wereprovided by a Bio-Rad FTS-6000 Fourier-Transform Infrared (FTIR)spectrophotometer, which was configured with a ceramic-coated globarsource and a Ge-coated KBr beam splitter. The hemispherical measurementgeometry is implemented by using a diffuse-gold coated 150 mm diameterintegrating sphere (Mid-IR IntegratIR-Pike Technologies), with thesamples mounted on a port cut into the surface of the sphere. Aliquid-nitrogen-cooled MCT detector is mounted on top of the sphere withits field of view restricted to a portion of the bottom surface of thesphere. The Mid-IR Integral IR features an 8 degree illumination of thesample and reflectance samples are placed directly onto the sample portof the upward-looking sphere or over a thin infrared transmittingwindow.

For reflectance measurement, square sections of samples approximately 40mm² were cut and mounted onto an 18 mm horizontal reflectance samplingport on the integrating sphere. A diffuse gold reference standard wasused in the measurement and all the samples were placed on a backermaterial made of dull black paint coated polymer. The spectrum of eachsample was collected with a rapid scan mode and 200 scans per sample.Three readings were taken for each sample and the resulting dataaveraged. To compensate for the signal loss due to the backer material,the sample reflectance was calculated according to ASTM:E903-96 standardtest method for Reflectance of materials using integrating sphere.

Transmittance of transparent or translucent materials in the region from2 μm to 17 μm was measured by placing the sample at the transmissionstation accommodating a standard 2″×3″ sample holder. The instrument wasthen set in the absolute measurement (100%) position, and the 100%signal without the sample in the measurement position is recorded. Thesample was then placed into position and the transmitted reading isrecorded. The transmitted signal divided by the 100% signal equals thetransmittance.

Table 1 contains the directional-hemispherical transmittance andreflectance data of all data points collected, averaged over thespectral ranges 3 μm-5 μm and 9 μm-14 μm.

Transmission Optical Density Test Method

For the purpose of this patent, visual opacity will be measured in termsof optical density (OD).

The transmission optical density at room temperature of the samples wasmeasured with a desktop densitometer model TRX-N instrument supplied bythe Tobias Associates, Inc., Ivyland Pa. U.S.A. The device consists of alight source and a silicon photodetector with a spectral response ofgreater than 20% between 475 nanometers and 675 nanometers. This deviceis capable of measuring the optical density of films in bothtransmission and reflection modes. Transmission mode was used for allmeasurements.

Optical density is a measurement that approximates the response of thehuman eye. Optical density is defined by the following equation:OD=Log 1/Twhere, OD=optical density, and T=transmission.

The instrument requires around 10 minutes of warm up time. The test areais approximately 3 mm in diameter, and the samples to be measured werelarge enough to completely cover the test area, The test procedure is asfollows

-   1. Place 0.0075 inch thick PET film standard over sample port.-   2. Zero is set by lowering the detector arm to the light port and    pressing the control button.-   3. The digital readout should read zero.-   4. Record the result.-   5. Place the test sample on the light table so that it covers the    light port.-   6. Lower the detector arm to the sample covering the light port and    press the control button.-   7. Read and record cord the result from the LED display.-   8. Repeat steps 5 through 8 for the remaining samples.

The optical density measurement is displayed on three 7 segment lightemitting diode display units, one for each digit. For the purpose ofthis patent, a material will be considered visibly opaque when the OD isgreater than 0.30 between 475 and 675 nm.

Emissivity Measurement Test Method

The infrared emittance near room temperature of the samples was measuredwith a portable emissometer model AE instrument supplied by the Devices& Services Company, (Texas, U.S.A). This emittance device determines thetotal thermal emittance, in comparison with standard high and lowemittance materials.

The Devices & Services emissometer, model AE, consists of a measuringhead and a scaling digital voltmeter. The measuring head is designed sothat its radiation detector is heated to 355K, allowing the test samplesto remain at ambient temperature during measurement. The radiationdetector is a differential thermopile with two high-ε and two low-ε, andthus responds only to heat transferred by radiation between itself andthe sample. The detector has a near-constant response to wavelengths ofinfrared radiation and views a 50-mm diameter area of a sample from adistance of 4.3 mm. The manufacturer specifies that the output voltageof the detector is linear with ε to within ±0.01 units and isproportional to T⁴ _(d)-T⁴ _(s), where T_(d) and T_(s) are the absolutetemperatures of the detector and test sample, respectively. Two“standards”, each 66.7 mm in diameter and 4 mm thick, are supplied withthe emissometer and have ε's of 0.06 and 0.90. The instrument requiresaround 60 minutes of warm up time. Because the emissometer iscomparative, it must be calibrated before use. The two standards areplaced on the heat sink so that both of them attain the ambienttemperature.

The detector head is then placed over the high emissivity standard andthe gain of the voltmeter is adjusted so that it reads 0.90, afterallowing about 90 seconds for equilibration. The detector head thenplaced over the low emissivity standard and the offset trimmer isadjusted such that the voltmeter reads 0.06. The adjustments arerepeated until the emissometer may be moved from one standard and theother and the voltmeter readings indicate the two values without anyadjustment.

To determine emissivity, a sample is cut in form and size similar to thestandards and then placed on the heat sink and allowed to equilibratewith it. The detector head is placed over it and the reading of thevoltmeter directly gives the hemispherical emittance of the testsurface. The emissometer model AE instrument measures the hemisphericalemittance approximately in the 3-30 μm wavelength ranges.

Radar Transparency

The radar transparency test of select examples of the present inventionwas conducted in accordance with ASTM Test Method D 4935-99. Thestandard fixture of this test method, having a test region with insidediameter of 1.3 inches and an outside diameter of 3.0 inches, providedaverage loss in dB from about 1 GHz to about 5 GHz,

The radar transmission measurements from 1 GHz to 20 GHz were conductedin a substantially similar manner with the following exception. Insteadof the standard test fixture, a 7 mm diameter coaxial cable connectorwas used as the test fixture. For this 1 GHz to 20 GHz test, a two-portvector network analyzer (VNA) with coaxial test cables attached to eachport. At the device under test (DUT) end of each cable would be ageneral precision grade coaxial connector of size 7 mm, based on theIEEE Std 287-2007. The VNA is setup to sweep from 500 MHz to 20 GHz,using 401 data points and the test cables or connected together as a“through” connection. The output is set to S21-LOGMAG, or the insertionloss in dB, and a “response” type calibration is performed. The testcables are then separated and the sample (cut to a ½ inch diameter) isplaced over the 7 mm interface and the test cables are reconnected.

The samples were measured as described above to obtain transmission dataaveraged from the range of 1 to 5 GHz and from the range 1 to 20 GHz,Samples were deemed radar transparent if the average transmissionthroughout the measured range was greater than 90%.

Samples of material prepared according to examples provided herein weretested, the loss in dB was recorded, and average radar percenttransmission was calculated by the following equation:% Transmission=[10^((dB loss/10))]×100The percent transmission in the reported ranges was reported in Table 3.Oil Repellency Test

In these tests, oil rating was measured using the AATCC Test Method118-1983 with the following modification. Because the second surface ofthe visually opaque, thermally transparent component of the presentinvention is typically attached to the thermally reflective component,only the first surface of the visually opaque, thermally transparentcomponent could be tested. Thus, the oil ratings reported herein are theresult of measurements made on first surface of the visually opaque,thermally transparent component of the construct. Three drops of thetest oil are placed on the sample surface. After 3 minutes, a numericaloil rating is assigned for the sample that corresponds to the highestnumber oil that does not wet/absorb into the sample. Higher numericalvalues indicate better oil repellency for the samples tested. Values of2 or more, 4 or more, 5 or more, and even 6 or more, are preferred whereoil repellency is desired.

Metal Thickness Test

The metal thickness of the thermally reflective layer and of the radarreflective layer, where applicable, was measured via an indirect methodfor samples prepared by physical vapor deposition using equipment andprocesses well known in the art. The thickness was determined by InficonSentinal III quartz crystal monitor that provides a deposition rate inangstroms per second. Based on the deposition time, the nominalthickness was calculated by multiplying the deposition time by thedeposition rate.

For samples having metal foil as the thermally reflective layer, themetal foil thickness was measured using a Mitutoyo No. 2804F-10micrometer prior to incorporation in the construct.

EXAMPLES Example 1

A sample of a construct was prepared comprising carbon-coated ePTFE andmetallized ePTFE, in the following manner.

A first component comprising carbon-coated ePTFE representing the firstsubstrate was prepared as described in Example 3 of U.S. PatentApplication Publication No. 2007/0009679 with the following exceptions.The ePTFE membrane used had a thickness of about 30 μm, a weight ofabout 9 grams per square meter, and an average pore size of about 0.2μm. The amount of carbon black used was about 0.9% by weight of ePTFEmembrane. Optical density and thermal reflection properties of the firstsubstrate of the first component were measured according to the testmethods herein, and reported in Table 1.

A second component comprising metallized ePTFE was prepared inaccordance with U.S. Pat. No. 5,955,175, representing the thermallyreflective layer. Emissivity was measured on the metallized sideaccording to the test methods herein, and reported in Table 1. The metalthickness of the metalized ePTFE of the thermally reflective layer wascalculated to be about 200 nm.

The first component was then placed against the metallized side of thesecond component, and a 0.5 mil layer of polyethylene film was placed inbetween. The layers were bonded together using a Geo Knight and Co.Model 178SU Heat Press at about 350° F. for about 10 seconds to form aconstruct. Multi-spectral test results for sample constructs preparedaccording to this example, and measured from the carbon-coated ePTFEside of the sample, are shown in Table 1 and shown in FIGS. 9, 10, and11. The constructs had a visible reflection of approximately 8%, a nIRreflection of approximately 12%, a MWIR reflection of approximately 28%,and a LWIR reflection of approximately 50% as reported in Table 1.

The spectral response curves in FIGS. 9, 10, and 11, show thevariability of reflectance and transmission over the broad range ofwavelengths tested. The average results reported are calculated from thedata in these figures over the specific wavelength ranges reported inTable 1. FIG. 11 additionally includes reflectance data on constructsfrom about 8 μm to about 9 μm.

Example 2

A sample of a construct was prepared comprising a layer of carbon-coatedePTFE, Al foil, and a textile backer as follows.

A first component of carbon-coated ePTFE was prepared as described inExample 1, representing the first substrate. Optical density and thermaltransmission properties of the first substrate were measured accordingto the test methods herein, and reported in Table 1.

A second component was prepared comprising a discontinuous layer of foiladhered to a textile backer, representing the thermally reflectivelayer. The second component was formed by perforating a layer of Altransfer foil from Crown Roll Leaf, Inc (part #MG39-100G) to provideapproximately 30% open area to form a discontinuous layer of transferfoil. The discontinuous layer of transfer foil was adhered to a textilebacker using a continuous thermoplastic polyurethane adhesive (8) toform the second component, representing the thermally reflective layer.The layers were bonded together using a Geo Knight and Co. Model 178SUHeat Press at about 280° F. for about 8 seconds. Emissivity was measuredon the discontinuous aluminum transfer foil side according to the testmethods herein, and reported in Table 1.

The first component was then placed on top of the foil side of thesecond component and bonded together using a heat press as described inExample 1, and portions of the polyurethane adhesive corresponding tothe open areas of the discontinuous layer of transfer foil adhereddirectly to the first component to form the construct. Multi-spectraltest results for the construct samples prepared according to thisexample, and measured from the first component side, are shown inTable 1. The constructs had a visible reflection of approximately 7%, anIR reflection of approximately 11%, a MWIR reflection of approximately31%, and a LWIR reflection of approximately 43%. The hand for thissample was measured by the hand test method described herein to be 186gm.

Example 3

A sample of a construct was prepared comprising a layer of coloredePTFE, Al foil and a textile backer as follows.

A first component was prepared by coloring a layer of 1.2 mil ePTFE(about 0.2 micron average pore size, and about 18 grams per squaremeter) with a single substantially continuous coating of black Sharpie®permanent marker to comprise the first substrate of the construct.Optical density and thermal transmission properties of the firstsubstrate were measured according to the test methods herein, andreported in Table 1.

A second component was prepared by perforating a layer of Al transferfoil from Crown Roll Leaf, Inc (part #MG39-100 G) to provideapproximately 30% open area to form a discontinuous layer of transferfoil to comprise the thermally reflective layer. The metal thickness ofthe Al transfer foil was calculated to be approximately 0.0008 inches.This discontinuous layer of transfer foil was adhered to a textilebacker using a continuous thermoplastic polyurethane adhesive. The foiland textile backer layers were bonded together using a Geo Knight andCo. Model 178SU Heat Press at about 280° F. for about 8 seconds.Emissivity was measured on the discontinuous aluminum transfer foil sideaccording to the test methods herein, and reported in Table 1.

The uncolored side of first component was placed on top of the foil sideof the second component, and the first and second components were bondedtogether using a heat press as described in Example 1 to form aconstruct. Portions of the polyurethane adhesive corresponding to theopen areas of the discontinuous layer of transfer foil adhered directlyto the first component.

Multi-spectral test results for samples of constructs prepared accordingto this example, and measured from the first component side, are shownin Table 1. The constructs had a visible reflection of approximately 5%,a nIR reflection of approximately 11%, a MWIR reflection ofapproximately 48%, and a LWIR reflection of approximately 43%.

Example 4

A sample of a construct was prepared comprising printed ePTFE andmetallized ePTFE in the following manner.

A first component of 1.2 mil ePTFE film (about 0.2 micron average poresize, and about 18 grams per square meter) was coated with an aqueoussolution of about 13% Rhodapex ES-2 from Rhodia, Inc. and about 6%hexanol, and allowed to dry. A color image was printed on the coatedePTFE film using an HP Designjet 110 plus printer to create the firstsubstrate. Optical density and thermal transmission properties of thefirst substrate of the first component were measured according to thetest methods herein, and reported in Table 1.

A second component of metallized ePTFE was prepared in accordance withU.S. Pat. No. 5,955,175 using gold as the metal and omitting theoleophobic coating to create the thermally reflective layer. Emissivitywas measured on the metallized side according to the test methodsherein, and reported in Table 1.

The unprinted side of the first component was bonded to the metallizedside of the second component using a 0.5 mil layer of polyethylene asdescribed in Example 1.

Multi-spectral test results for samples of constructs prepared accordingto this example and measured from the first component side, are shown inTable 1 and shown in FIGS. 9, 10, and 11. The constructs had a visiblereflection of approximately 38%, a nIR reflection of approximately 62%,a MWIR reflection of approximately 60%, and a LWIR reflection ofapproximately 47%, as reported in Table 1. The spectral response shownin FIG. 11 shows that constructs having printing on the ePTFE firstcomponent effects the reflectance in the visible wavelength regionprimarily between 250 nm to 600 nm.

Example 5

A sample of a construct was prepared substantially according to Example1 with the following exceptions.

In place of a carbon-coated ePTFE layer, a first component was preparedby coloring a layer of 1.2 mil ePTFE (about 0.2 micron average poresize, and about 18 grams per square meter) with a single substantiallycontinuous coating of black Sharpie® permanent marker to create thefirst substrate of the first component. Optical density and thermaltransmission properties of the first substrate were measured accordingto the test methods herein, and reported in Table 1.

Emissivity was measured on the metallized side of a second componentprepared and tested as in Example 1 according to the test methodsherein, and reported in Table 1.

The uncolored side of the first component was then bonded to themetallized side of the second component using a discontinuouspolyurethane adhesive. A textile was then laminated to thenon-metallized side of the second component using a discontinuouspolyurethane adhesive to form a construct. Multi-spectral test resultsfor samples prepared according to this example were measured from thefirst component side, and are shown in Table 1 and shown in FIGS. 9, 10,and 11. The constructs had a visible reflection of approximately 5%, anIR reflection of approximately 12%, a MWIR reflection of approximately53%, and a LWIR reflection of approximately 54%, as reported in Table 1.

A sample prepared according to this Example was radar transparent havingan average transmission of about 100% both throughout the range of 1-5GHz and throughout the range of 1-20 GHz, when tested by the methodprovided herein. The sample was also tested for Hand measurements,weight in grams per square meter (gsm), and oleophobicity, according tothe methods provided herein. The results are provided in Table 3.

Example 6

A sample of a construct comprising two layers of a carbon-coated ePTFE,joined by a metal coating was prepared in the following manner.

A sample of carbon-coated ePTFE prepared as described in Example 1,representing the first substrate of the first component. Optical densityand thermal transmission properties of the first substrate were measuredaccording to the test methods herein, and reported in Table 1.

The carbon-coated ePTFE first substrate of the first component wasdivided into two roughly equal sections. One section was painted withKrylon Interior/exterior gold metallic spray paint (Part No. 1510-H597)in accordance with the directions on the can to create the thermallyreflective layer. The non-carbon coated side of the remainingnon-painted section was placed over the wet paint of the other sectionand smoothed by hand to remove wrinkles, allowing the paint to act bothas an adhesive and low emissivity component to form a composite sample.The sample was allowed to dry for about 10 minutes, and the emissivitywas measured using a Devices and Services, Inc. (10290 Monroe Drive#202, Dallas, Tex. 75229) model AE emissometer.

Multi-spectral test results for samples of constructs prepared accordingto this example were measured from the first specimen side, and areshown in Table 1. The constructs had a visible reflection ofapproximately 9%, a nIR reflection of approximately 13%, a MWIRreflection of approximately 31%, and a LWIR reflection of approximately41%.

A sample prepared according to this Example was radar transparent havingan average radar transmission of about 100% both throughout the range of1-5 GHz and throughout the range of 1-20 GHz, when tested by the methodsprovided herein. The sample was also tested for Hand measurements,weight in grams per square meter (gsm), and oleophobicity, according tothe methods provided herein. The results are provided in Table 3.

Example 7

A sample of a construct comprising polypropylene and metal was preparedin the following manner.

A first substrate of the first component was prepared by coloring oneside of a layer of 2.5 mil polypropylene film with a substantiallycontinuous coating of black Sharpie® permanent marker. Optical densityand thermal transmission properties of the first substrate were measuredaccording to the test methods herein, and reported in Table 1.

A thermally reflective layer was prepared comprising a metallized ePTFEmaterial substantially in accordance with U.S. Pat. No. 5,955,175.Emissivity was measured on the metallized side according to the testmethods herein, and reported in Table 1.

The uncolored side of the first substrate was then bonded to themetallized side of the thermally reflective layer using a Geo Knight andCo. Model 178SU Heat Press at about 350° F. for about 10 seconds to forma construct.

Multi-spectral test results for samples of constructs prepared accordingto this example as measured from the colored side are shown in Table 1and shown in FIGS. 9, 10, and 11. The constructs had a visiblereflection of approximately 7%, a nIR reflection of approximately 16%, aMWIR reflection of approximately 43%, and a LWIR reflection ofapproximately 78%, as reported in Table 1.

Example 8

A sample of a construct of metallized polyurethane was prepared in thefollowing manner.

A first substrate comprising a sample of 1 mil polyurethane film(Deerfield Urethanes, Part No. 1710S, Deerfield, Mass.), was metallizedusing physical vapor deposition. Approximately 300 nm of aluminum wasdeposited on the second surface of the first substrate by physical vapordeposition. This sample was then colored on the non-metallized side witha single substantially continuous coating of black Sharpie® permanentmarker.

The first substrate sample properties were measured utilizing anon-metallized portion of the substantially Sharpie® marker coated PUfilm. Optical density and thermal transmission properties of thissubstrate were measured according to the test methods herein, andreported in Table 1 as a ‘“first component”.

Multi-spectral test results for samples of constructs prepared accordingto this example were measured from the colored side, and are shown inTable 1. The constructs had a visible reflection of approximately 7%, anIR reflection of approximately 13%, a MWIR reflection of approximately54%, and a LWIR reflection of approximately 18%.

Example 9

A sample of a construct was prepared comprising a polyethylene film andaluminum foil in the following manner.

A first component was prepared by coloring a layer of 2.0 milpolyethylene film with a single substantially continuous coating ofblack Sharpie® permanent marker to comprise the first substrate of afirst component. Optical density and thermal transmission properties ofthe first substrate were measured according to the test methods herein,and reported in Table 1.

A second component comprising Stor-It™ brand aluminum foil was used asthe thermally reflective layer. The metal thickness of the aluminum foilused for this thermally reflective layer was calculated to beapproximately 0.001 inches. Emissivity was measured according to thetest methods herein, and reported in Table 1.

The uncolored side of the PE film was placed adjacent to the aluminumfoil, and utilized as the multi-spectral, selectively reflectiveconstruct. Multi-spectral test results for samples of the constructprepared according to this example were measured from the colored side,and are shown in Table 1 and shown in FIGS. 9, 10, and 11. Theconstructs had a visible reflection of approximately 7%, a nIRreflection of approximately 23%, a MWIR reflection of approximately 70%,and a LWIR reflection of approximately 73%, as reported in Table 1.

A sample prepared according to this Example was not radar transparent,having an average transmission of about 0% throughout the range of 1-5GHz and throughout the range of 1-20 GHz, when tested by the methodprovided herein. The sample was also tested for Hand measurements,weight in grams per square meter (gsm), and oleophobicity, according tothe methods provided herein. The results are provided in Table 3.

Example 10

A sample of a construct was prepared substantially according to Example5 with the following exception. In place of the discontinuouspolyurethane adhesive, the first and second components were bondedtogether using a continuous coating of 3M Super 77™ adhesivemultipurpose adhesive. The textile backer was also omitted.

Optical density and thermal transmission properties of the firstsubstrate of the first component as prepared in Example 5, were measuredaccording to the test methods herein, and reported in Table 1.

Emissivity of the second component was measured on the metallized sideas in Example 5 according to the test methods herein, and reported inTable 1.

Multi-spectral test results for samples of constructs were measured fromthe colored side, and are shown in Table 1. This embodiment of thepresent invention had a visible reflection of approximately 4%, a nIRreflection of approximately 9%, a MWIR reflection of approximately 34%,and a LWIR reflection of approximately 16%.

Example 11

A sample of a construct was prepared substantially according to Example8, substituting 1.5 mil polyethylene terephthalate (PET) film for thepolyurethane film, Emissivity was measured from the non-metallized side,and the values are reported in Table 1 for the thermally reflectivelayer.

As in Example 8, the first substrate properties were measured utilizinga non-metallized portion of the substantially Sharpie® marker coated PETfilm. Optical density and thermal transmission properties of thissubstrate were measured according to the test methods herein, andreported in Table 1 as the “first component”.

Multi-spectral test results for samples of constructs prepared accordingto this example were measured from the colored side, and are shown inTable 1. The constructs had a visible reflection of approximately 7%, anIR reflection of approximately 17%, a MWIR reflection of approximately63%, and a LWIR reflection of approximately 5%.

Example 12

A sample of a construct was prepared comprising ePTFE and a metallizedePTFE in the following manner.

A first component of 1.2 mil ePTFE film (about 0.2 micron average poresize, and about 18 grams per square meter) was measured for opticaldensity and thermal transmission properties according to the testmethods herein, and reported in Table 1.

A second component comprising metallized ePTFE was prepared inaccordance with U.S. Pat. No. 5,955,175, representing the thermallyreflective layer. Emissivity was measured on the metallized sideaccording to the test methods herein, and reported in Table 1.

The first component was then placed against the metallized side of thesecond component, and a 0.5 mil layer of polyethylene film was placed inbetween. The layers were bonded together using a Geo Knight and Co.Model 178SU Heat Press at about 350° F. for about 10 seconds to form theconstruct. Multi-spectral test results for samples of the constructprepared according to this example, and measured from the carbon-coatedePTFE side of the sample, are shown in Table 1 and shown in FIGS. 9, 10,and 11.

The constructs had a visible reflection of approximately 86%, a nIRreflection of approximately 73%, a MWIR reflection of approximately 56%,and a LWIR reflection of approximately 83%, as reported in Table 1.

Example 13

A sample of a construct was prepared comprising carbon-coated ePTFE andmetallized polyester in the following manner.

A sample was prepared by providing a first component of carbon-coatedePTFE as in Example 1 as the first substrate. A second component ofNi/Cu metallized polyester taffeta from Laird Co. (Product #3027-217)representing the thermally reflective layer (30) was then placedadjacent to the first substrate. The product specification sheet listedthe metal thickness of this Ni/Cu metalized polyester taffeta as 152 μm.Multi-spectral test results for samples of the construct preparedaccording to this example were measured from the first component side,and are shown in Table 1, and shown in FIGS. 9, 10, and 11. Theconstructs had a visible reflection of approximately 10%, a nIRreflection of approximately 15%, a MWIR reflection of approximately 44%,and a LWIR reflection of approximately 61%, as reported in Table 1.

A sample prepared according to this Example was not radar transparent,having an average transmission of about 0% throughout the range of 1-5GHz and throughout the range of 1-20 GHz, when tested by the methodprovided herein. The sample was also tested for Hand measurements,weight in grams per square meter (gsm), and oleophobicity, according tothe methods provided herein. The results are provided in Table 3.

Example 14

Gore part # WJIX102108HZ was obtained to measure the multi-spectralreflective properties of the composite. The Gore part is representativeof a military specification compliant fabric with acceptable visual andnIR performance, but no requirement of thermal reflectance properties.The fabric is a camouflage printed textile laminated to a bicomponentfilm with a backer textile. Each color of the 4 color pattern—Light tan,Urban tan, Light Coyote, and Highland—was measured as 14 a, 14 b, 14 c,and 14 d, respectively. The multi-spectral test results are given inTable 1. Reflectance on the scale of FIGS. 10 and 11 is in the range of0.0 to 1.0, which correlates to a reflectance percentage between 0 and100%, as reported in the examples and Table 1.

TABLE 1 Measurements of Sample Properties. First Component ThermallyTotal Total Reflective Construct Optical Transmission Transmission LayerTotal Reflection Example Density (3-5 μm) (9-12 μm) Emissivity Vis NIR3-5 μm 9-12 μm  1 1.95 62.7 73.4 0.12 7.8 11.7 28.4 50.0  2 1.95 62.773.4 0.38 6.8 10.5 30.9 42.5  3 4.15 74.3 71.3 0.38 4.8 11.1 48.3 42.8 4 2.53 81.1 67.2 0.08 38.1 61.5 59.8 47.0  5 4.15 74.3 71.3 0.12 5.412.1 53.0 53.7  6 1.95 62.7 73.4 0.34 9.4 13.4 30.8 41.1  7 1.08 67.085.7 0.12 7.4 16.4 42.5 77.7  8 1.19 55.0 22.1 0.04 6.9 12.6 54.2 17.9 9 1.07 70.2 77.6 0.02 6.9 23.4 70.2 72.9 10 4.15 74.3 71.3 0.12 4.2 8.934.2 16.3 11 1.09 60.8 18.7 0.02 7.0 17.1 62.5 5.1 12 0.75 90.8 86.10.12 86.1 72.6 56.4 82.9 13 1.95 62.7 73.4 0.15 9.8 14.8 43.8 61.3 14 a— — — — 28.9 52.1 11.9 3.9 14 b — — — — 23.6 47.9 9.7 7.1 14 c — — — —13.8 35.0 9.7 7.0 14 d — — — — 8.9 35.9 9.9 6.8

TABLE 2 Moisture Vapor Transmission Rate Measured For Samples. ExampleMVTR (g/m²/day) 5 >14000 6 >8000 13 >21000

TABLE 3 Radar Transparency Reported in Percent Transmission,Oleophobilicity, Weight and Hand Measurements. % % Example TransmissionTransmission Oleo- Weight Hand No. At 1-5 GHz at 1-20 GHz phobicity(gsm) (gm) 5 100 100 2 147 304 6 100 100 6 40 50 9 0 0 4 75 73 13 0 0 5107 111

We claim:
 1. A method for making a radar transparent, thermally andvisually camouflaging construct, comprising the steps of: a. providing afirst substrate comprising a thermally transparent first microporouspolymeric material having a first surface and a second surface; b.providing a colorant; c. applying the colorant to at least the firstsurface of the first substrate to form a thermally transparent, visuallyopaque layer; d. providing a second substrate comprising a lowemissivity component; e. orienting the low emissivity component of thesecond substrate towards the second surface of the first substrate; f.adhering the first and second substrates to form a construct having anaverage reflection of <70% in the wavelength range of 400 nm-600 nm, anaverage reflection of >25% in the wavelength range of and 9 μm-12 μm,and a radar transmission greater than 90% in the frequency range from 1GHz to about 20 GHz.
 2. The method of claim 1 wherein the thermallytransparent polymeric material comprises ePTFE.
 3. The method of claim 2comprising printing a colorant on the ePTFE to form the thermallytransparent, visually opaque layer.
 4. The method of claim 1 wherein thesecond substrate comprises a second microporous polymeric layer and themethod further comprises the step of vapor depositing a metal onto thesecond microporous layer.
 5. The method of claim 4 comprising the stepof affixing the first and second microporous layers together.
 6. Themethod of claim 1 wherein the second substrate comprises a secondmicroporous polymeric layer and the method further comprises the step ofspraying a metal onto the second microporous layer.
 7. The method ofclaim 6 comprising the step of adhering the first and second microporouslayers together applying the metal spray as an adhesive.
 8. The methodof claim 1 comprising laminating at least one additional layer on a sideof the construct proximate the second substrate.
 9. The method of claim8 wherein the at least one additional layer is a textile layer.
 10. Themethod of claim 8 wherein the at least one additional layer is a radarcamouflaging layer.